Semiconductor device having diode devices with different barrier heights and manufacturing method thereof

ABSTRACT

A Schottky diode device includes a substrate having a first conductivity type, a first well region having a second conductivity type disposed in the substrate, and a first doped region having the second conductivity type in the first well region, wherein the first doped region includes a first portion and a second portion, and the first portion and the second portion have different doping concentrations. The first portion includes a region having at least four sides, from a top-view perspective, abutting the second portion.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/222,464 filed Dec. 17, 2018, now U.S. Pat. No. 10,658,456, which is acontinuation of U.S. patent application Ser. No. 15/793,439 filed Oct.25, 2017, now U.S. Pat. No. 10,157,980, which applications are herebyincorporated by reference.

BACKGROUND

Schottky barrier diodes, or simply Schottky diodes, are widely used inmodern semiconductor devices. The Schottky diode enjoys lots ofadvantages such as a low forward voltage drop and a high switchingspeed. The Schottky diode is particular useful in radio-frequencyapplications, for example, energy harvest devices. Most of the time asemiconductor device may require a few Schottky diodes with differentspecifications for performing different tasks or fulfilling differentperformance requirements. Fabricating processes for such similar yetdifferent Schottky diodes may be time-consuming and costly. Accordingly,it is desirable to improve existing manufacturing procedures of theSchottky diodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. Specifically, the dimensions ofthe various features may be arbitrarily increased or reduced for clarityof discussion.

FIGS. 1A through 1L are top views and cross-sectional views ofintermediate stages of a method of manufacturing a semiconductor device,in accordance with some embodiments.

FIGS. 2A through 2C are schematic top views of intermediate stages of amethod of manufacturing a semiconductor device, in accordance with someembodiments.

FIG. 3 is a chart showing the performance comparison for thesemiconductor device in FIG. 1, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides structures and manufacturing operationsof diode, specifically a Schottky barrier diode device, according tovarious embodiments. A diode with a lower barrier height may provide ahigher forward conduction current while also resulting in a higherreverse current. A diode with a higher forward conduction current may bedesirable in many applications, but the accompanying higher reversecurrent may hinder its popularity. As a result, diodes with differentperformance specifications (e.g., barrier heights) in a samesemiconductor chip are commonly seen in modern electronic applications.Existing methods call for individual lithography operations to achievedifferent barrier heights for different diode devices. In the presentdisclosure a manufacturing operation is proposed to produce a variety ofdiode devices on a same semiconductor wafer or chip. Different diodeswith varying barrier heights are manufactured during a same lithographyoperation and using a same photomask, and the lithography operationsrepeated according to the different barrier heights required for thediodes are prevented accordingly. Both the manufacturing cost andproduction through put are improved effectively.

FIGS. 1A through 1L are top views and cross-sectional views ofintermediate stages of a method of manufacturing a semiconductor device100, in accordance with some embodiments. Each figure contains at leastone of subplots (A), (B) and (C) where the subplot (A) shows across-sectional view of the semiconductor device 100 across a dioderegion 110 and a transistor region 120, and subplots (B) and (C) show atop view and a cross-sectional view of the diode region 110,respectively. The subplots (A) and (C) are taken along sectional linesAA′ and BB′, respectively, of subplot (B), in which subplot (A) furtherincludes the aforesaid transistor region 120 not shown in subplot (B).In some of the subsequent figures, subplot (C) is omitted forsimplicity.

Referring to FIG. 1A, a substrate 102 is provided or received. Thesubstrate 102 includes a semiconductor material such as silicon,germanium, silicon germanium, silicon carbide, gallium arsenide, or thelike. Alternatively, the substrate 102 includes a compound semiconductorincluding gallium arsenic, gallium phosphide, indium phosphide, indiumarsenide, indium antimonide, or combinations thereof. In otheralternatives, the substrate 102 may include a doped epitaxial layer, agradient semiconductor layer, and/or a semiconductor layer overlayinganother semiconductor layer of a different type, such as a silicon layeron a silicon germanium layer. The substrate 102 may be doped with anN-type dopant, such as arsenic, phosphor, or the like, or may be dopedwith a P-type dopant, such as boron or the like.

Next, isolation structures 104 are formed on the substrate 102. Theisolation structures 104 are formed in both the diode region 110 and thetransistor region 120. As shown in the subplot (A), the diode region 110is partitioned into several zones by the isolation structures 104, i.e.,an anode zone 110A, two bulk zones 110B, and two cathode zones 110C. Theanode zone 110A, bulk zones 110B, and cathode zones 110C are separatedand surrounded by the isolation structures 104 near an upper surface 103of the semiconductor device 100. The isolation structures 104 may beshallow trench isolation (STI) or local oxidation of silicon (LOCOS). Asan exemplary operation for manufacturing the isolation structures 104,several trenches are formed initially by an etching operation, such as adry etching, a wet etching, a reactive ion etching (RIE) operation, orthe like. Next, isolation materials are filled into the trenches to formthe isolation structures 104. The isolation materials may be formed ofelectrically insulating materials, such as dielectric materials. In someembodiments, the isolation structures 104 are formed of oxide, nitride,oxynitride, silicon dioxide, nitrogen-bearing oxide, nitrogen-dopedoxide, silicon oxynitride, polymer, or the like. The dielectric materialmay be formed using a suitable process such as chemical vapor deposition(CVD), physical vapor deposition (PVD), atomic layer deposition (ALD),thermal oxidation, UV-ozone oxidation, or combinations thereof. In someembodiments, a planarization operation, such as grinding or chemicalmechanical planarization (CMP) processes, may be used to remove excessmaterials of the isolation structures 104 and level the top surfaces ofthe isolation structures 104 with the substrate 102.

Referring to FIG. 1B, well regions 106 and 108 are formed in the dioderegion 110. Further, a well region 152 is formed in the transistorregion 120. In an embodiment, the well region 106 covers the anode zone110A, the cathode zones 110C, and the region under the isolationstructure 104. The well region 108 covers the bulk zone 110B. Similarly,the well region 152 is formed in the transistor region 120. The wellregions 106, 108 and 152 may be formed by implanting dopants by one ormore ion implantation operations 105. Ions or dopants are implanted todesired portions of the upper surface 103 of the substrate 102. In someembodiments, a mask may be used to permit only the desired portions toreceive dopants. In the present embodiments, the well regions 106, 108and 152 are adjacent to the isolation structures 104. In someembodiments, the well regions 106, 108 and 152 are surrounded by theisolation structures 104 when viewed from above, as shown in the subplot(A). In the depicted embodiment, adjacent well regions 106 and 108 areseparated near the upper surface 103 by at least one isolation structure104 and abut each other at a level lower than that of the isolationstructures 104.

Referring to FIG. 1C, a photomask 122 is positioned over thesemiconductor device 100. The photomask 122 is used for patterning thewell region 106. In an embodiment, the photomask 122 is configured topartially expose the well region 106 while covering the remainingportion of the semiconductor device 100. For example, the anode zone110A and the cathode zones 110C are partially exposed while the bulkzones 110B and the transistor region 120 are completely covered. In anembodiment, the photomask 122 includes openings substantiallyoverlapping the well region 106. In an embodiment, the openings of thephotomask 122 may be hollow portions or formed of relatively transparentmaterials. The amount of the well region 106 that is exposed can becontrolled through different design parameters of the openings of thephotomask 122. In the depicted example, the photomask 122 includes aplurality of strips 122A over the well region 106. The strips 122A actas masks to prevent ions from implanting into the well region 106 andmay abut one another if no exposure spacing is present. To conduct ionimplantation, strip-like openings 122B are formed between the strips122A and allow ions to pass through. In an embodiment, the strips 122Aare arranged in a parallel fashion. Consequently, the strip-likeopenings 122B are also formed as parallel strips or slits. In anembodiment, the strip-like openings 122B or the strips 122A run over theisolation structures 104 between the anode zone 110A and the cathodezone 110C. Each of the strips 122A has a width W1. A gap S1 betweenadjacent thinned strips 122A is defined as the dimension of each of thestrip-like openings or slits 122B. In an embodiment, the ratio of thespacing S1 to the width W1, i.e., S1/W1, or the proportion S1:W1,determines an exposure opening ratio (equivalent proportion S1:W1) ofthe photomask 122. For example, a ratio of 0% (or proportion 0:1) meansno opening is present while a ratio of 100% (or S1:W1=1:1) implies ahalf-opened photomask over the well region 106. In an embodiment, theexposure opening proportion is between about 33.3% (i.e., S1:W1=1:3) andabout 300% (i.e., S1:W1=3:1) in order to obtain desirable diffusionoutcome given the thermal budget described below. In an embodiment, thestrip 122A is seen as a spacing between the slits 122B. In anembodiment, the width W1 of the strips 122A is regarded a spacing widthbetween the slits 122B.

In an embodiment, the exposure opening proportion is defined as aproportion between a summed area of the openings 122B overlapping theexposed well region 106 and a total area of the covering regions 122Aoverlapping with the well region 106. An area ratio of 0% or areaproportion (0:1) means no opening is present while an area ratio of 100%or area proportion (1:1) implies a half-opened photomask over the wellregion 106. In an embodiment, the area proportion of the openings 122Bto the covering regions 122A is between about 1:3 and about 3:1. Asdifferent diodes are manufactured with different exposure opening ratioson the same photomask 122, several well regions including the wellregion 106 may receive different amounts of implantation dopantsassuming all well regions have a same area under identical implantationconditions, for example, same implantation dose. Varying dopingconcentrations in different well regions may be obtained throughappropriate smoothing operations to average the doping concentrations inthe well regions. Different shapes and numbers of the openings 122B ofthe photomask 122 are possible and are within the contemplated scope ofthe present disclosure.

Subsequently, an ion implantation operation 107 is performed on thesemiconductor device 100. The semiconductor device 100 after receivingthe ion implantation operation 107 is shown in FIG. 1D. Ions areimplanted into the well region 106 through the openings 122B of thephotomask 122. An implanted first portion 112B (marked in shades) isformed in the well region 106 by the ion implantation operation 107. Thefirst portion 112B substantially follows the pattern of the spacings122B of the photomask 122. The first portion 112B has a strip-likepattern overlapped with the anode zone 110A and the cathode zones 110C,and the strip-like pattern follows the exposure pattern of the photomask122. As seen in subplots (B) and (C), a second portion 112A between thestrips of the first portion 112B is left undoped in the well region 106.The second portion 112A substantially follows the pattern of the stripstructure 122A of the photomask 122. In the depicted example as shown insubplot (A), the first portion 112B has a doping depth less than thedepth of the well region 106. In an embodiment, the first portion 112Bhas a depth less than the depth of the isolation structure 104. In anembodiment, the first portion 112B has a substantially uniform dopingprofile across each of the strips of the second portion 112A. In anembodiment, the strips of the second portion 112A are substantially voidof implanted ions of the first portion 112B as a result of the ionimplantation operation 107.

Still referring to FIG. 1D, each of the well regions 106 and 152 mayinclude dopants of a first conductive type (for example, N-type), suchas phosphorus or the like. The well region 108 may include dopants of asecond conductive type (for example, P-type), such as boron or the like.In some embodiments, the conductive type of the well region 106, 108 or152 may be identical to or opposite of the conductive type of thesubstrate 102. For example, the substrate 102 and the well region 108may be of P-type while the well regions 106 and 152 may be of N-type. Inan embodiment, the implanted ions of the ion implantation 107 have thefirst conductive type or the second conductive type. In an embodiment,the dose of the ion implantation 107 is between about 1E13 atoms/cm² andabout 1E15 atoms/cm². In an embodiment, the dose of the ion implantation107 is between about 1E14 atoms/cm² and about 1E15 atoms/cm². In anembodiment, the energy power of the ion implantation operation 107 isbetween about 5 and about 30 Key for a P-type dopant, and is betweenabout 5 and 50 Key for an N-type dopant.

The quantity of the implanted ions received by the first portion 112B isdetermined by the area ratio of the openings 122B to the well region 106exposed through the upper surface 103 for a given uniform implantationsource. A Schottky diode (e.g., the diode region 110) may include aheterojunction constructed by an anode terminal (e.g., the anode zone110A) formed of a metallic material and a cathode terminal (e.g., thecathode zone 110B) formed of a semiconductor layer (e.g., first dopedlayer 112 in FIG. 1E) in a well region (e.g., the well region 106). Thebarrier height of the Schottky diode is determined by both theconductive type and the doping concentration of the semiconductor layer.When ions of a same conductive type are selected for the first portion112B and the well region 106, such as an N-type dopant, a higher dopingconcentration leads to a lower barrier height. In contrast, using theimplantation ions of opposite conductive types for the first portion112B and the well region 106 causes a greater barrier height as thedoping concentration increases.

Referring to FIG. 1E, a thermal operation 109 is performed on thesubstrate 102. The thermal operation 109 may include an annealingoperation, such as a furnace anneal, a rapid thermal anneal (RTA) or thelike. Through the thermal operation 109, ions in the first portion 112Bare driven out and diffuse into the adjacent second portion 112A. Thedoping concentration in the first portion 112B is decreased along withthe ion diffusion, and the doped concentration of the second portion112A is increased accordingly. Therefore, a contiguous first dopedregion 112 is formed, across which a substantially uniform dopingconcentration is achieved due to ion diffusion. In an embodiment, thefirst doped region 112 is formed on the upper surface 103 of the anodezone 110A and the cathode zones 110C. The eventual diffusion performanceof the implanted ions is determined by at least the initial dopingconcentration of the first portion 112B and the dimensions of thespacings 122B of the photomask 122. The diffused distance of ions may becontrolled by the thermal budget of the thermal operation 109 and thedopant species used. In an example, the diffusion distances of thecommonly used dopants may be boron>phosphorous>arsenic under a samethermal condition. In an embodiment, the thermal operation 109 has athermal budget of a heating temperature between about 1000° C. and about1100° C. for a duration between about 5 seconds and about 20 seconds. Insome examples with a strip shape of the spacing 122B, the eventualdoping concentration is controlled by the exposure opening ratio S1/W1in FIG. 1C. In an embodiment, the spacing S1 is no greater than about0.5 μm.

As discussed previously, the quality of the first doped region 112 isdetermined by the diffusion performance of the ions between the firstportion 112B and the second portion 112A. Thus, it is required to takethe diffusion distance into account that is dependent on the thermalbudget and the dopant type. Assuming the average ion diffusion distanceis L, the maximum length of the width W1 would be designed around 2 Lsuch that the ions situated at the edge of the first portion 112B couldreach the center of the second portion 112A through diffusion and form afirst doped region 112 without dopant-free area. Similarly, the maximumlength of the spacing S1 would be around 2 L such that the ions drivenfrom the thermal operation 109 could leave the first portion 112B andreach the neighboring strip of the second portion 112A. The first dopedregion 112 with a substantially uniformly doping profile is obtainedaccordingly.

In an embodiment which provide a thermal budget permitting an averagediffusion distance L for dopants at the edge of the first portion 112B,a range of the exposure opening proportion S1:W1 is between about 33.3%(i.e., S1:W1=1:3) and about 300% (i.e., S1:W1=3:1). In an embodiment, anexposure opening ratio is defined as a ratio of the implanted openingwidth S1 to the summed width of the width S1 and the non-implanted stripW1, i.e., S1:(S1+W1). In an embodiment, the exposure opening ratioS1:(S1+W1) is determined as between about 25% and about 75% in order toobtain desirable diffusion outcome.

FIGS. 1F and 1G illustrate a forming of transistors in the transistorregion 120. In the present embodiment, only one transistor 150 is shown.However, any number of transistors or other active/passive devices arewithin the contemplated scope of the present disclosure. Referring toFIG. 1F, a gate layer 154 is initially formed on the upper surface 103.The gate layer 154 may comprise conductive materials, such aspolysilicon or metallic materials. In some embodiments, the metallicmaterial may include tungsten (W), titanium nitride (TiN), tantalum(Ta), or compounds thereof. Other commonly used metals that could beused in the conductive material include nickel (Ni) and gold (Au).Furthermore, the gate layer 154 may be formed by an operation such asCVD, PVD, sputtering, or the like. In an embodiment, a thermal operation111 is performed on the substrate 102 to treat the sidewall surface ofthe gate layer 154. The thermal operation 111 may include an annealingoperation, such as a furnace anneal, a rapid thermal anneal (RTA) or thelike. The operation parameters of the thermal operation 111 may besimilar to those of the thermal operation 109. In an embodiment, inorder to treat the sidewall surface of the gate layer 154, the thermaloperation 111 has a thermal budget of a heating temperature betweenabout 750° C. and about 900° C. for a duration between about 10 minutesand about 60 minutes.

Next, two lightly doped regions (or lightly doped drains, LDD) 158 areformed in the well region 152 between the gate layer 154 and theisolation structures 104. The lightly doped regions 158 may be formed byusing an ion implantation operation similar to the operation 107 whilesome implantation parameters, such as the doping concentration, may bevaried. In an embodiment, the lightly doped regions 158 have aconductive type that is the same as or different from that of the wellregion 152. In an embodiment, the thermal operation 111 is employedagain to treat the lightly doped regions 158 subsequent to the formationof the lightly doped regions 158. The operation parameters of thethermal operation 111 may be similar to those used for the thermaloperation 109. In an embodiment, in order to activate the lightly dopedregions 158, the thermal operation 111 has a thermal budget of a heatingtemperature between about 700° C. and about 800° C. for a durationbetween about 30 minutes and about 90 minutes.

In an embodiment, a gate dielectric layer (not separately shown) isformed between the gate layer 154 and the substrate 102. The gatedielectric layers may be formed of dielectric materials, such as siliconoxide, silicon nitride, silicon oxynitride, high-k dielectric material,or the like. The high-k material may be selected from metal oxides,metal nitrides, metal silicates, transition metal-oxides, transitionmetal-nitrides, transitional metal-silicates, oxynitride of metals,metal aluminates, zirconium silicate, zirconium aluminate, hafniumoxide, or combinations thereof. The gate dielectric layer may be formedby any suitable method, such as CVD, PVD, ALD, plasma-enhanced CVD(PECVD), high-density plasma CVD (HDPCVD), low-pressure CVD (LPCVD), orthe like.

Subsequently, as illustrated in FIG. 1G, spacers 156 are formed on asidewall of the gate layer 154. In an embodiment, the spacers 156 areformed of a dielectric material such as oxide, oxynitride, nitride,nitrogen-bearing oxide, nitrogen-doped oxide or silicon oxynitride. Thespacers 156 may be formed by depositing a blanket dielectric materialcovering the gate material 154 and the upper surface 103, followed by anetching operation to remove the horizontal portions of the dielectricmaterial.

Referring to FIG. 1H, an ion implantation operation 115 is performed onthe cathode zones 110C of the diode region 110. In an embodiment,another photomask (not separately shown) is employed to expose only thecathode zones 110C while covering the remaining portions of thesemiconductor device 100. Two second doped regions 116 are formed in thecorresponding cathode zones 110C accordingly. In an embodiment, thesecond doped region 116 is used to improve electrical properties of thecathode zones 110C and conductively couples the cathode zones 110C to acathode terminal. In an embodiment, the ion implantation operation 115supplies a substantially uniform concentration across each of thecathode zones 110C, e.g., using a photomask with an exposure openingratio of 100%. The second doped region 116 has a conductive type same asthat used in the well region 106, such as an N-type dopant. In anembodiment, the implantation operation 115 of arsenic dopants has a dosebetween about 1E15 atoms/cm² and about 6E15 atoms/cm² with an energypower between about 10 Key and 30 Key. In an embodiment, theimplantation operation 115 of phosphorous dopants has a dopingconcentration between about 5E13 atoms/cm³ and about 5E14 atoms/cm³ withan energy power between about 10 Key and 60 Key. In an embodiment, thecathode zones 110C receive a thermal operation in order to activate theions and make the implantation profile more uniform. Such thermaloperation may include an annealing operation, such as a furnace anneal,a rapid thermal anneal (RTA) or the like. In an embodiment, the thermaloperation 109 is performed after the formation of the second dopedregions 116. In an embodiment, the thermal operation 109 is repeatedafter the second doped regions 116 are completed.

Referring to FIG. 1I, an ion implantation operation 117 is performed onthe bulk zones 110C of the diode region 110. In an embodiment, yetanother photomask (not separately shown) is employed to expose only thebulk zones 110B while covering the remaining portions of thesemiconductor device 100. Two third doped regions 118 are formed on thecorresponding bulk zones 110B accordingly. In an embodiment, the thirddoped region 118 is used to improve electrical properties of the bulkzones 110B and conductively couples the bulk zones 110B to a bodyterminal. In an embodiment, the ion implantation operation 117 suppliesa substantially uniform concentration across each of the bulk zones110B, e.g., using a photomask with an exposure opening ratio of 100%. Inan embodiment, the third doped layer 118 has a conductive type same asthat of the well region 108, such as a P-type dopant. In an embodiment,the implantation operation 117 of boron dopants has a dose between about1E15 atoms/cm² and about 6E15 atoms/cm² with an energy power betweenabout 3 Key and 30 Key. In an embodiment, the bulk zone 110B receives athermal operation 131 in order to activate the ions and make theimplantation profile more uniform. The thermal operation 131 may includean annealing operation on the substrate 102, such as a furnace anneal, arapid thermal anneal (RTA) or the like. In an embodiment, in order toactivate the third doped region, the thermal operation 131 applied tothe entirety of the substrate 102 has a thermal budget of a heatingtemperature between about 1000° C. and about 1100° C. for a durationbetween about 5 seconds and about 20 seconds.

In an embodiment, a fourth doped region 119 is formed at a periphery ofthe anode zone 110A. The fourth doped region 119 may be formed duringthe formation of the third doped regions 118 (a modification to thephotomask may be needed for forming the fourth doped region 119accompanying the formation of the third doped regions 118). The fourthdoped region 119 may be used to reduce the amount of leakage current ofthe first doped region 112 around the edges. In an embodiment, thefourth doped region 119 is formed on the upper surface 103. In anembodiment, the fourth doped region 119 has a depth less than that ofthe first doped region 112. In an embodiment, the fourth doped region119 has a conductive type opposite to the conductive type of the wellregion 106.

In FIG. 1J, two source/drain regions 160 are formed in the well region152 between the isolation structures 104 and the gate layer 154. Thesource/drain regions 160 may be formed by an ion implantation operation.In an embodiment, the source/drain regions 160 are formed with the gatelayer 154 and the isolation structures 104 as implantation masks. Insome embodiments, the source/drain regions 160 are of a conductive type,such as N-type, opposite to the conductive type of the well region 152.The source/drain regions 160 may be formed with their upper surfacesubstantially level with the upper surface 103. Alternatively, a raisedsource/drain structure may also be used. In an embodiment, thesource/drain regions 160 receive a thermal operation 133 in order toactivate the implanted ions and make the implantation profile moreuniform. The thermal operation 133 may include an annealing operation onthe substrate 102, such as a furnace anneal, a rapid thermal anneal(RTA) or the like. In an embodiment, in order to activate thesource/drain regions 160, the thermal operation 133 has a thermal budgetof a heating temperature between about 1000° C. and about 1100° C. for aduration between about 5 seconds and about 20 seconds.

As discussed previously, during the manufacturing operations of thetransistor 150, one or more thermal operations (e.g., operations 111,131 and 133) may be utilized to activate the ions of the lightly dopedregions 158 and the source/drain regions 160 and achieve better dopingprofiles. In the meantime, such thermal operations can be simultaneouslyapplied to the first doped region 112, the second doped regions 116 orthe third doped regions 118 subsequent to the thermal operation 109. Inan embodiment, the first doped region 112, which is formed through iondiffusion between the first portion 112B and the second portion 112A, isobtained through several thermal operations as mentioned above. Duringthe manufacturing procedures of the semiconductor device 100, calculatedthermal budget demonstrated in several thermal operations for heatingexisting features in either the diode region 110 or the transistorregion 120 could accumulatively provide the implanted ions in the firstportion 112B of the first doped region 112 with sufficient thermalenergy to diffuse into its neighboring regions, for example, the secondportion 112A of the first doped region 120. As long as the overallthermal budget is met, as previously discussed, extra annealingoperations or prolonged annealing duration may not affect the finalquality of the first doped region 112. In an embodiment, the thermaloperations are conducted through, for example, heating the entirety ofthe semiconductor device 100 or the substrate 102. Such thermaloperation causes most of the doped regions to be heated at the sametime. As a result, the performance of the first doped region 112, thesecond doped regions 116 or the third regions 118 may be improved in aneconomical manner through the multiple thermal operations.

Subsequently, a conductive layer 124 is formed on the diode region 110and the transistor region 120, as shown in FIG. 1K. Specifically, theconductive layer 124 is formed on the anode zone 110A, the cathode zones110C and the bulk zone 110B of the diode region 110. The conductivelayer 124 is also formed on the source/drain regions 160 of thetransistor 150. In an embodiment, the conductive layer 124 is ametal-containing conductive layer, e.g., a silicide layer. In anembodiment, the conductive layer 124 acts as an anode material in theanode zone 110A of the Schottky diode. In an embodiment, the conductivelayer 124 abuts the first doped region 112 acting as the semiconductorlayer, thereby a Schottky barrier interface is formed between theconductive layer 124 and the first doped region 112. A barrier height isestablished at the interface accordingly. In an embodiment, theconductive layer 124 is employed to provide a reduced-resistance contactbetween a subsequently-formed conductive via and underlying layers (suchas the second doped regions 116, the third doped regions 118 or thesource/drain regions 160).

When a silicide layer is selected as the conductive layer 124, thesilicide layers 124 may be formed of tungsten silicide, titaniumsilicide, cobalt silicide, nickel silicide and the like. Taking tungstensilicide as an example, the silicide layer is formed by reactingtungsten fluoride (WF₆) with silane (SiH₄). Alternatively, the silicidelayer may be formed by depositing a layer of selected metal over thesilicon portion of the above-mentioned doped regions, followed by anannealing operation so as to facilitate silicidation of the selectedmetal. In some embodiments, portions of the metal layer not reactingwith the silicon may be removed.

Referring to FIG. 1L, an inter-layer dielectric (ILD) 138 is formed overthe substrate 102. The ILD 138 may be formed with a variety ofdielectric materials and may be, for example, oxide, oxynitride, siliconnitride, nitrogen-bearing oxide, nitrogen-doped oxide, siliconoxynitride, polymer, or the like. The ILD 138 may formed by any suitablemethod, such as CVD, PVD, spin coating, or the like.

Several conductive vias are formed in the ILD 138. One or moreconductive vias 132 formed over the anode zone 110A electrically couplethe conductive layer 124 at the anode zone 110A with an anode terminal(not separately shown). Conductive vias 134 formed over the cathodezones 110C electrically couple the cathode zones 110C with a cathodeterminal (not separately shown). Also, conductive vias 136 formed overthe bulk zones 110B electrically couple the bulk zones 110B with a bodyterminal (not separately shown). Additionally, although notdemonstrated, each of the source/drain regions 160 is electricallycoupled to a corresponding conductive via. The conductive vias 132, 134and 136 may be formed by forming recesses through the ILD 138 by anetching operation. A conductive material may be filled into the recessesto electrically connect the underlying structures (e.g., doped regions112, 116, 118 or 160). The conductive material of the conductive vias132, 134 and 136 may include, but is not limited to, titanium, tantalum,titanium nitride, tantalum nitride, copper, copper alloys, nickel, tin,gold, or combinations thereof.

Once the conductive vias 132, 134 and 136 are in place, several contactpads 172 are formed thereon. Each of the contact pads 172 may have awidth larger than the corresponding conductive vias 132, 134 and 136. Insome embodiments, the contact pads 172 are disposed over the ILD 138.Subsequently, an interconnect structure 170 is formed over the ILD 138and the contact pads 172. The interconnect structure 170 is configuredto electrically couple the substrate 102 with overlaying featuresthrough the contact pads 172. The interconnect structure 170 may includemultiple metal layers 176. Each of the metal layers 176 may includehorizontal conductive wires and vertical metal vias where the horizontalmetal lines are electrically coupled to adjacent overlaying orunderlying horizontal metal lines through at least one vertical metalvia. The metal layers 176 may include conductive materials such asnickel, tin, gold, silver, alloys or combinations thereof.

The metal layers 176 are electrically insulated from other components.The insulation may be achieved by insulating materials, such as adielectric 174. The dielectric 174 may be formed of oxides, such asun-doped Silicate Glass (USG), Fluorinated Silicate Glass (FSG), siliconoxide, silicon nitride, silicon oxynitride, low-k dielectric materials,or the like.

FIGS. 2A through 2C are schematic top views of intermediate stages of amethod of manufacturing a semiconductor device 200, in accordance withsome embodiments. Some features in FIGS. 2A through 2C that share labelswith reference numerals in FIGS. 1A through 1L indicate the features aresimilar in materials or manufacturing operations. Referring to FIG. 2A,the semiconductor device 200 shown in subplots (A) and (B) is similar tothe semiconductor device 100 shown in FIG. 1C, except that thesemiconductor device 200 further includes a diode region 210 adjacent toor away from (not shown) the diode region 110. The diode region 210includes a well region 206 abutting the diode region 110 through thewell region 108. Further, the diode region 210 includes another wellregion 208 in the semiconductor 102 on a side of the well region 206opposite the well region 108. Like the diode region 110, the dioderegion 210 includes an anode zone 210A and two cathode zones 210C in thewell region 206, and a bulk zone 210B in the well region 208. Aphotomask 222 is used to expose both of the well regions 106 and 206. Inan embodiment, the photomask 222 includes a first exposure opening ratiopattern and a second exposure opening ratio pattern. The first exposureopening ratio pattern includes the first plurality of strips 122A overthe well region 106 and openings 122B between the strips 122A. A firstexposure ratio is determined by the ratio of the width of the strip 122Aand the width of the opening 122B. The second exposure opening ratiopattern includes the second plurality of strips 222A disposed over thewell region 206 and openings 222B between the strips 222A that partiallyexpose the well region 206. A second exposure ratio is determined by theratio of the width of the strip 222A and the width of the opening 222B.

In an embodiment, an ion implantation operation 107 similar to that usedin FIG. 1C is performed on the semiconductor device 200 across the dioderegions 110 and 210. In some embodiments, the manufacturing operationsfor the diode regions 110 as illustrated in FIGS. 1A through 1L aresimilarly applied to the diode region 210 of the semiconductor device200.

In an embodiment, the first photomask 222 includes at least two exposureopening proportions for the well regions 106 and 206. For example, for aslit-shaped structure in the exposure opening design, the exposureopening proportions for the well regions 106 and 206 can be defined asS1/W1 and S2/W2, respectively. Through appropriate setting of theopening proportions, the semiconductor device 200 can have at least twodiode devices on a wafer that have different barrier heights by usingonly a single photomask and a single ion implantation operation.

Referring to FIG. 2B, a different photomask 222 configuration is shownwith different opening shapes. The photomask 222 has a first exposureopening ratio pattern and a second exposure opening ratio pattern thatinclude a plurality of concentric rectangular rings 122A and 222A overthe well regions 106 and 206, respectively. Spacings 122B and 222B areformed to expose the respective well regions 106 and 206. The exposureopening proportion can be defined as a ratio of the area of the openings122B (222B) overlapping the exposed well region 106 to a total area ofthe rectangular rings 122A (222A) overlapping with the well region 106(206). Alternatively, assume each of the concentric rectangles has asame side width W3 or W4, and a spacing S3 or S4 is defined as a gapbetween two parallel sides of adjacent rectangles. The line widths andthe spacings of the concentric rectangular concentric rectangles 122A or222A can be tuned to control the opening ratio S3/W3 or S4/W4. ReferringFIGS. 1D, 2A and 2B, a concentric photomask exposure opening design mayhelp formation of a concentric shape of the first portion 112B in thefirst doped region 112. The second portion 112A can receive diffusedions of the surrounding doped portion 112B from both of the vertical andhorizontal directions, rather than from only the vertical directions ofthe strip-like doped region 112B (demonstrated in FIG. 1D). In anembodiment, a single photomask may include different exposure openingshapes for different well regions on a same semiconductor device, a samewafer or chip.

Referring to FIG. 2C, the photomask 220 is configured with anotherconfiguration of opening shapes. The photomask 220 has a first exposureopening ratio pattern and a second exposure opening ratio pattern thatinclude grids 122A and 222A over the well regions 106 and 206,respectively. An array of rectangular spacings 122B and 222B is formedaccordingly to expose the respective well regions 106 and 206. Theexposure opening proportions can be defined as a ratio between an areaof the openings 122B (222B) overlapping the exposed well region 206 anda total area of the grid 232A (242A) overlapping with the well region106 (206). The grid widths and the dimensions of the hollow rectangles122B and 222B can be tuned to control their exposure opening ratios. Inan embodiment, the spacing between the openings 232B (i.e., the width ofa grid bar 232A) in the diode region 110 is less than the spacingbetween the openings 242B (i.e., the width of a grid bar 242A) in thediode region 210. Referring FIGS. 1D, 2A and 2C, a grid-like photomaskexposure opening design may help formation of a grid doped region in thefirst portion 112B. The second portion 112A can receive diffused ions ofthe surrounding doped portion 112B from both of the vertical andhorizontal directions, rather than from only the vertical directions ofthe strip-like doped region 112B.

FIG. 3 is a chart showing a performance comparison for the semiconductordevice 100 in FIG. 1, in accordance with some embodiments. The currentvalues under different photomask exposure opening proportions areillustrated. The conductive type of the semiconductor layer (e.g., firstdoped region 112 in FIG. 1D) in a diode region is set as different fromthat of the well region (e.g., the well region 106 in FIG. 1D). Astrip-like opening design as shown in FIG. 1C is employed in FIG. 3.Measurements are taken under the forward biasing of about 0.15 volts andreverse biasing of about 2.0 volts for the forward current and reversecurrent measurement, respectively. FIG. 3 shows that as the photomaskhas a higher exposure opening proportion, the Schottky barrier height isincreased, therefore a lower forward current is reached. This trend canalso be observed in photomask exposure opening proportion cases of 2:1,1:1 and 1:2 where under the same doping intensity and bias, diodes withsmaller opening proportions, i.e., receiving less dopants as a whole,generates greater forward current because the Schottky barrier is lesshigh. As discussed previously, when the conductive types of thesemiconductor layer and the well region are different, a higher dopingconcentration will lead to a higher barrier height. In other words, alower conduction current is thus obtained. The measurement result showsthat as the well region is exposed with a fully-opened proportion of1:0, both the forward current and the reverse current are minimalcompared to other cases with lower opening proportions (e.g., between2:1 and 0:1). The measurement result verifies that an openingproportion-tunable photomask as proposed can help formation of multiplediodes in a same wafer using a same hard mask Different effective dopingconcentrations in different diode regions are obtained through one ormore subsequent thermal operations. As a result, the manufacturing costand the number of photomasks for a variety of diodes with differentbarrier heights can be kept as minimal as possible.

According to an embodiment of the present disclosure, a Schottky diodedevice includes a substrate having a first conductivity type, a firstwell region having a second conductivity type disposed in the substrate,and a first doped region having the second conductivity type in thefirst well region, wherein the first doped region includes a firstportion and a second portion, and the first portion and the secondportion have different doping concentrations. The first portion includesa region having at least four sides, from a top-view perspective,abutting the second portion.

According to an embodiment of the present disclosure, a Schottky diodedevice includes a substrate, a first well region in the substrate, and afirst doped region in the first well region, wherein the first dopedregion comprises a first portion and a second portion alternating witheach other, and the first portion and the second portion have differentdoping concentrations.

According to an embodiment of the present disclosure, a Schottky diodedevice includes a substrate having a first conductivity type, a firstwell region having a second conductivity type disposed in the substrate,and a first doped region having the second conductivity type in thefirst well region, wherein the first doped region including a firstportion and a second portion, and the first portion and the secondportion have different doping concentrations. The Schottky diode devicealso includes a second doped region having the second conductivity typeover the first doped region in the first well region, wherein the firstdoped region defines a first zone and a second zone separated from thefirst zone, and the second doped region is disposed in the second zone.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A Schottky diode device, comprising: a substratehaving a first conductivity type; a first well region having a secondconductivity type disposed in the substrate; and a first doped regionhaving the second conductivity type in the first well region, the firstdoped region comprising a first portion and a second portion, and thefirst portion and the second portion having different dopingconcentrations, wherein the first portion comprises a region having atleast four sides, from a top-view perspective, abutting the secondportion.
 2. The Schottky diode device according to claim 1, furthercomprising a metal containing layer on the first doped region.
 3. TheSchottky diode device according to claim 1, further comprising anisolation structure disposed in the substrate and at least surroundingthe first well region from a top view perspective.
 4. The Schottky diodedevice according to claim 1, wherein the first conductive type isdifferent from the second conductive type.
 5. The Schottky diode deviceaccording to claim 1, wherein the first well region defines an anodezone and a cathode zone, and each of the anode zone and the cathode zoneoverlaps the first doped region.
 6. The Schottky diode device accordingto claim 5, further comprising a second doped region disposed in thecathode zone and exposed from an upper surface of the substrate.
 7. TheSchottky diode device according to claim 5, further comprising a thirddoped region on an upper surface of the substrate at a periphery of theanode zone and having the first conductive type.
 8. The Schottky diodedevice according to claim 5, wherein the first portion and the secondportion extends through the anode zone and the cathode zone.
 9. TheSchottky diode device according to claim 1, further comprising: a gatelayer on the substrate; source/drain regions in the substrate on twosides of the gate layer; and a lightly doped region (LDD) in thesubstrate between the gate layer and the respective source/drainregions.
 10. The Schottky diode device according to claim 1, wherein thefirst portion comprises concentric rings alternatingly arranged withconcentric rings of the second portion.
 11. A semiconductor device,comprising: a substrate; a first well region in the substrate; and afirst doped region in the first well region, wherein the first dopedregion comprises a first portion and a second portion alternating witheach other, and the first portion and the second portion have differentdoping concentrations.
 12. The semiconductor device according to claim11, wherein the first portion comprises a plurality of first concentricrings and the second portion comprises a plurality of second concentricrings.
 13. The semiconductor device according to claim 12, wherein eachof the first concentric rings has a first width, and each of the secondconcentric rings has a second width different from the first width. 14.The semiconductor device according to claim 11, wherein the firstportion comprises a plurality of first strips having a third width, thesecond portion comprises a second plurality of strips having a fourthwidth, and a ratio between the third width and the fourth width is fromabout 1:3 to about 3:1.
 15. The semiconductor device according to claim11, further comprising: a second well region in the substrate; and asecond doped region within the second well region, wherein the seconddoped region comprises a third portion and a fourth portion alternatingwith the third portion, wherein a first area ratio between the firstportion and the second portion is different from a second area ratiobetween the third portion and the fourth portion.
 16. The semiconductordevice according to claim 11, further comprising an isolation structureextending in the substrate and defining the first well region, whereinthe first doped region has a depth less than the isolation structure.17. The semiconductor device according to claim 16, wherein the firstwell region extends below the isolation structure.
 18. The semiconductordevice according to claim 11, further comprising a metal-containinglayer on the first doped region.
 19. A Schottky diode device,comprising: a substrate having a first conductivity type; a first wellregion having a second conductivity type disposed in the substrate; afirst doped region having the second conductivity type in the first wellregion, the first doped region comprising a first portion and a secondportion, and the first portion and the second portion having differentdoping concentrations; and a second doped region having the secondconductivity type over the first doped region in the first well region,wherein the first doped region defines a first zone and a second zoneseparated from the first zone, and the second doped region is disposedin the second zone.
 20. The Schottky diode device according to claim 19,wherein both of the first portion and the second portion extends acrossthe first zone and the second zone.